1G-GTE Full Boost 5000+ RPM

Hi Guys, hoping to get a few ideas as to why my motor really struggles to spool the turbo.

Car: Toyota AE85 Trueno

Engine: 1G-GTE engine (2 litre straight 6) TVIS removed, 1G-GZE pistons, NA cams with adjustable cam gears

EFI: Link G4+ Fury ECU, Bosch 440cc injectors, NZEFI smart coils

Current turbo: Garrett GTX3071r Turbo

Sinco customs exhaust manifold

Turbosmart 45mm waste gate, Boost control solenoid

2.5’’ exhaust

2.5’’ intercooler piping

Turbosmart Race port BOV

Front facing intake plenum with factory runners. Factory throttle body

4.5 diff ratio

The dyno graphs are from when I was running a turbonetics GTK325 turbo with 0.63 exhaust housing. Changing to the bigger gtx3071r turbo made no change to the boost curve; it made a nice change to the power curve though.

The engine seems to run really well but for whatever reason it just doesn’t get moving until 5000+ RPM. Reading on other forums, there are reports of this engine and turbo combination making full boost by 4000 RPM.

I’m currently in the process of swapping in another factory turbo 1G-GTE engine to see if the issue is with the current motor itself. A good time to check over things with it all apart, if anyone has some insight. I have attached the dyno sheets. I have some logs I can attach if anyone is interested.

Cheers, Rory

Hi Rory, I’ve got this feeling it has something to do with those cams you have in the engine. Do you have anymore information on them?

The cams are from a 1G-GE, the NA variant of these motors. They have slightly more lift. We played around with the cam timing on the dyno but weren't able to bring the boost on any earlier.

The first thing to do is the obvious stuff. Do a boost leak test by pressurizing your charge pipes. Check for exhaust leaks.

Still, you need to remember the big picture. You have a 2 liter engine which has been modified to sacrifice low end torque for high end horsepower.

1. Deleting TVIS makes worse low end torque. You don't have the velocity of air at low rpm.

2. Using higher lift cams means you have later intake valve closing. That means you are trapping less air at low rpm.

3. The adjustable cam gears - you would need to advance the intake side and retard the exhaust side for better low end torque. It may not spool better but you will at least trap more air. And you will give up high end power. That's why VVT-i came about.

The other thing to consider is the exhaust side. A 3 inch exhaust will help spool. A smaller turbine A/R will help spool. To check your exhaust side, lug the engine in 5th gear from 1000rpm to 4000rpm (if you can do this safely). This allows maximum time for spool without having to worry about the inertia of the compressor wheel. With a smaller turbine A/R you will make more boost in this manuever.